Assessment of the Effect of Pollen Grains of Maize (Zea Mays L.) on Cercospora Arachidicola Hori. and on Infection of Leaves of Groundnut (Arachis Hypogea L.) caused by the Fungus

Abstract

Conidia of Cercospora arachidicola are straw-coloured or olivaceous, subfusiform, multicellular, 28.3-68.1(jm in lengths. They contain 3-7 cells. They germinated in distilled water and at 85-100% R.H. The optimum pH for germination was 5.0-6.0; any cell of the conidium germinating produced only one germ tube. The germ tube commonly comes from the end cells with occasional germ tube emerging from one or two median cells. Pollen of Zea mays, glucose (1.0-8.0%) and peptone (0.1-2.0%) failed to stimulate more median cells to germinate. Maize pollen, however, stimulated germination of the conidia at pH 3 and 10. During germination tests using conidia in water drops on sterile glass slides, the conidia germinated better and produced slightly longer germ tubes in the absence of pollen grains of Zea mays than in the presence of both non-sterile and autoclaved pollen grains. Particularly with the sterile pollen grains, percentage germination decreased with increasing pollen density. Maize pollen when added to solutions of glucose (1.0-8.0%) and peptone (0.1-2.0%) did not improve germination of the conidia. Conidia in pollen-free aqueous suspension drops on leaflets of groundnuts also germinated well than in suspension drops containing the pollen. Percentage germination in the presence of the pollen on leaflets with reduced fungal flora (a third of the original) and bacterial flora (a sixth of the original) was still lower than in the absence of pollen Maize pollen at moderate densities did not alter the infection rate of groundnut by C. arachidicola but high density of pollen on non-sterile groundnut leaves encouraged excessive phylloplane microfloral population which suppressed germ tube growth. Conidia stored at 0, 20, 40, 60, and 80% R.H. survived better during the initial 30 days at 20, 40 and 60% R.H. than at 0 and 80% R.H. The pattern of survival changed thereafter and conidia stored at 0% R.H. showed the highest survival on the 50th day; 35.1 percentage viability at 0% R.H. decreased with increasing relative humidity to 29.2% at 80% R.H. Maize pollen could not rejuvenate the aged conidia. It was concluded that since maize pollen reduced percentage germination o f C. arachidicola conidia, and high pollen density suppressed germ tube growth on non-sterile groundnut leaves, a closer spacing of maize plants in mixed farms could be recommended to encourage greater pollen deposit on the groundnut plants. This would be an environmentally friendly control measure provided the conidia of the other Cercospora leaf spot fungus, Cercospora personata, are similarly affected by maize pollen.